The invention relates to a gasification system and a process for the production of synthesis gas by partial combustion of a carbonaceous feed.
The carbonaceous feed can for instance comprise pulverized coal, biomass, (heavy) oil, crude oil residue, bio-oil, hydrocarbon gas or any other type of carbonaceous feed or mixture thereof.
Syngas, or synthesis gas, as used herein is a gas mixture comprising hydrogen, carbon monoxide, and potentially some carbon dioxide. The syngas can be used, for instance, as a fuel, or as an intermediary in creating synthetic natural gas (SNG) and for producing ammonia, methanol, hydrogen, waxes, synthetic hydrocarbon fuels or oil products, or as a feedstock for other chemical processes.
The disclosure is directed to a system comprising a gasification reactor for preparing syngas, and a quench chamber for receiving the syngas from the reactor. A syngas outlet of the reactor is fluidly connected with the quench chamber via a tubular diptube. Partial oxidation gasifiers of the type shown in, for instance, U.S. Pat. Nos. 4,828,578 and 5,464,592, include a high temperature reaction chamber surrounded by one or more layers of insulating and refractory material, such as fire clay brick, also referred to as refractory brick or refractory lining, and encased by an outer steel shell or vessel.
A process for the partial oxidation of a liquid, hydrocarbon-containing fuel, as described in WO9532148A1, can be used with the gasifier of the type shown in the patent referenced above. A burner, such as disclosed in U.S. Pat. Nos. 9,032,623, 4,443,230 and 4,491,456, can be used with gasifiers of the type shown in the previously referred to patent to introduce liquid hydrocarbon containing fuel, together with oxygen and potentially also a moderator gas, downwardly or laterally into the reaction chamber of the gasifier.
As the fuel reacts within the gasifier, one of the reaction products may be gaseous hydrogen sulfide, a corrosive agent. Molten or liquid slag may also be formed during the gasification process, as a by-product of the reaction between the fuel and the oxygen containing gas. The reaction products and the amount of slag may depend on the type of fuel used. Fuels comprising coal will typically produce more slag than liquid hydrocarbon comprising fuel, for instance comprising heavy oil residue. For liquid fuels, corrosion by corrosive agents and the elevated temperature of the syngas is more prominent.
Slag is also a well known corrosive agent and gradually flows downwardly along the inside walls of the gasifier to a water bath. The water bath cools the syngas exiting from the reaction chamber and also cools any slag that drops into the water bath.
Before the downflowing syngas reaches the water bath, it flows through an intermediate section at a floor portion of the gassification reactor and through the dip tube that leads to the water bath.
The gasifier as described above typically also has a quench ring. A quench ring may be formed of a corrosion resistant material, such as chrome nickel iron alloy or nickel based alloy such as Incoloy®, and is arranged to spray or inject water as a coolant against the inner surface of the dip tube. The gasifiers of U.S. Pat. No. 4,828,578 and U.S. Pat. No. 5,464,592 are intended for a liquid fuel comprising a slurry of coal and water, which will produce slag. Some portions of the quench ring are in the flow path of the downflowing molten slag, and the quench ring can thus be contacted by molten slag. The portions of the quench ring that are contacted by slag may experience temperatures of approximately 1800° F. to 2800° F. (980 to 1540° C.). The prior art quench ring thus is vulnerable to thermal damage and thermal chemical degradation. Depending on the feedstock, slag may also solidify on the quench ring and accumulate to form a plug that can restrict or eventually close the syngas opening. Furthermore any slag accumulation on the quench ring will reduce the ability of the quench ring to perform its cooling function.
In one known gasifier the metal floor portion of the reaction chamber is in the form of a frustum of an upside down conical shell. The metal floor may be made of the same pressure vessel metallurgy as the gasifier shell or vessel. The intermediate section may comprise a throat structure at a central syngas outlet opening in the gasifier floor.
The metal gasifier floor supports refractory material such as ceramic brick, that covers the metal floor, and also supports the refractory material that covers the inner surface of the gasifier vessel above the gasifier floor. The gasifier floor can also support the underlying quench ring and dip tube.
A peripheral edge of the gasifier floor at the intermediate section, also know as a leading edge, may be exposed to the harsh conditions of high temperature, high velocity syngas (which may have entrained particles of erosive ash, depending on the nature of the feedstock) and slag. Herein, the amount of slag may also depend on the nature of the feedstock.
In a prior art gasification system, the metal floor suffered wastage in a radial direction (from the center axis of the gasifier), beginning at the leading edge and progressing radially outward until the harsh conditions created by the hot syngas are in equilibrium with the cooling effects of the underlying quench ring. The metal wasting action thus progresses radially outward from a center axis of the gasifier until it reaches an “equilibrium” point or “equilibrium” radius.
The equilibrium radius is occasionally far enough from the center axis of the gasifier and the leading edge of the floor such that there is a risk that the floor can no longer sustain the overlying refractory. If refractory support is in jeopardy, the gasifier may require premature shut down for reconstructive work on the floor and replacement of the throat refractory, a very time intensive and laborious procedure.
Another problem at the intermediate section or throat section of the prior art gasifier is that the upper, curved surface of the quench ring is exposed to full radiant heat from the reaction chamber of the gasifier, and the corrosive and/or erosive effects of the high velocity, high temperature syngas which can include ash and slag. Such harsh conditions can also lead to wastage problems of the quench ring which, if severe enough, can force termination of gasification operations for necessary repair work. This problem is exacerbated if the overlying floor has wasted away significantly, exposing more of the quench ring to the hot gas and slag.
It was reported that the above described design had experienced frequent failures such as wearing off and corrosion of the refractory bricks, metal floor and the quench ring. The throat section, i.e. the interface between the reactor and the quench section, may have the following problems:                the metal supporting structure at the bottom of the intermediate section and reactor outlet is vulnerable to wear caused by the high temperature and corrosive hot gas;        the interface between the hot dry reactor and the wet quench area is vulnerable to fouling; and        the quench ring has a risk of overheating by hot syngas.        
U.S. Pat. No. 4,801,307 discloses a refractory lining, wherein a rear portion of the flat underside of the refractory lining at the downstream end of the central passage is supported by the quench ring cover while a front portion of the refractory lining overhangs the vertical leg portion of the quench ring face and cover. The overhang slopes downward at an angle in the range of about 10 to 30 degrees. The overhang provides the inside face with shielding from the hot gas. A refractory protective ring may be fixed to the front of an inside face of the quench ring.
U.S. Pat. No. 7,141,085 discloses a gasifier having a throat section and a metal floor with a throat opening at the throat section, the throat opening in the metal floor being defined by an inner peripheral edge of the metal gasifier floor. The metal gasifier floor has an overlying refractory material, and a hanging refractory brick at the inner peripheral edge of the metal floor having a bottom portion including an appendage, the appendage having a vertical extent being selected to overhang a portion of the inner peripheral edge of the metal gasifier floor. A quench ring underlies the gasifier floor at the inner peripheral edge of the gasifier floor, the appendage being sufficiently long to overhang the upper surface of the quench ring.
U.S. Pat. No. 9,057,030 discloses a gasification system having a quench ring protection system comprising a protective barrier disposed within the inner circumferential surface of the quench ring. The quench ring protection system comprises a drip edge configured to locate dripping molten slag away from the quench ring, and the protective barrier overlaps the inner circumferential surface along greater than approximately 50 percent of a portion of an axial dimension in an axial direction along an axis of the quench ring, and the protective barrier comprises a refractory material.
U.S. Pat. No. 9,127,222 discloses a shielding gas system to protect the quench ring and the transition area between the reactor and the bottom quench section. The quench ring is located below the horizontal section of the metal floor of the gasification reactor.
According to patent literature, one of the most common corrosion spots is at the front of the quench ring, which is the device that injects a film of water on the inside of the dip tube at the point where the refractory ends. The quench ring is not only directly exposed to the hot syngas, but may also suffer from insufficient cooling when gas collects in the top, and thermal overload and/or corrosion can occur.
Long term operation of the prior art designs described above has indicated a few issues. For instance, the designs protect the metal floor by refractory layers from the hot face side, yet the hot syngas can still ingress through the joints of the refractory brick and eventually reach the metal floor. The refractory brick may be eroded or worn off, in which case the protection of the metal floor will be lost. In addition, although the overhanging brick of the prior art is meant to protect the quench ring, the risk of overheating the quench ring is still relatively high as the brick, and its overhanging section, may be eroded. Industry has reported damages and cracks at the quench ring even with overhanging bricks. Finally, the syngas from the reactor typically contains soot and ash particles, which may stick on dry surface and start accumulating, for instance on the quench ring. The soot and ash accumulation at the quench ring may block the water distributor outlet of the quench ring. Once the water distribution of the quench ring is disturbed, the dip tube can experience dry spots and resulting overheating, resulting again in damage to the diptube.
In addition, the material of the dip tube is protected with a water film on the inner surface of the dip tube, which prevents the buildup of deposits and cools the wall of the dip tube. Inside the dip tube, severe corrosion may occur in case wall sections of the dip tube are improperly cooled or experience alternating wet-dry cycles.